The invention relates to a CDMA mobile telecommunications system, a base station and a method for receiving CDMA mobile telecommunications signals.
Mobile telecommunications systems are typically designed as cellular communications networks. Each cell comprises a base station. The mobile stations located within a cell communicate with the respective base station, which in turn forwards the signals, e.g., via a fixed network. CDMA mobile telecommunications systems (CDMA=Code Division Multiple Access) use code division multiplex in what is known as the spread spectrum instead of frequency division multiplex. This makes it possible for one base station to control more mobile stations within a cell of equal size.
CDMA is also used in UMTS (Universal Mobile Telecommunications System), IS95 and CDMA2000. To further increase the capacity of cellular mobile telecommunications systems and better adopt the systems to the topological conditions, so-called micro cells and macro cells are used. Micro cells are located completely within macro cells. A macro cell can contain a plurality of micro cells. Micro cells are used, for example, in areas with a very high density of mobile stations, e.g. in cities. In addition, there are also cells known as pico cells, which are primarily used for coverage within buildings. In principle, mobile stations within a macro cell require higher transmitting power than mobile stations within a micro cell. In each micro cell and each macro cell, an antenna is used to form a substantially circular or sectored reception area. Mobile stations within a macro cell communicate exclusively with the base station of the macro cell as long as they are not located within the reception area of a micro cell. If the mobile station gets into the reception area of a micro cell, a so-called handover is executed and the mobile station then communicates exclusively with the base station of the micro cell at clearly lower transmitting power.
Below, an inventive CDMA mobile telecommunications system according to Claim 1 with micro cells and macro cells is presented. The micro cells ore located within the macro cells. At least one micro cell is capable of attenuating the reception of at least one undesirable signal that has entered the micro cell from outside the micro cell. If a mobile station is located within a macro cell but outside a micro cell within this macro cell, the mobile station communicates exclusively with the base station of the macro cell. High transmitting power is required to maintain communication. Depending on the position of the mobile station within the macro cell, a situation may occur in which the high transmitting power of the mobile station has a negative effect on the reception within the micro cell. This may be the case particularly if the distance of the mobile station to the base station of the micro cell is smaller than the distance to the base station of the macro cell. According to the invention, the reception within the micro cell is then attenuated in the direction of the interfering mobile station. The reception of signals from mobile stations that are located within the micro cell and are sending with low transmitting power is then no longer impaired by the high transmitting power of the mobile station outside the micro cell. Advantageously, so-called null steering is used to generate null positions in the reception area of the micro cell.
Advantageous embodiments of the invention are set forth in the dependent claims.